Ferrocenyl-substituted tetrahydrothiophenes via formal [3 + 2]-cycloaddition reactions of ferrocenyl thioketones with donor-acceptor cyclopropanes

Ferrocenyl thioketones reacted with donor-acceptor cyclopropanes in dichloromethane at room temperature in the presence of catalytic amounts of Sc(OTf)3 yielding tetrahydrothiophene derivatives, products of formal [3 + 2]-cycloaddition reactions, in moderate to high yields. In all studied cases, dimethyl 2-arylcyclopropane dicarboxylates reacted with the corresponding aryl ferrocenyl thioketones in a completely diastereoselective manner to form single products in which (C-2)-Ar and (C-5)-ferrocenyl groups were oriented in a cis-fashion. In contrast, the same cyclopropanes underwent reaction with alkyl ferrocenyl thioketones to form nearly equal amounts of both diastereoisomeric tetrahydrothiophenes. A low selectivity was also observed in the reaction of a 2-phthalimide-derived cyclopropane with ferrocenyl phenyl thioketone

(4 + 3)-Cycloaddition of Donor-Acceptor Cyclopropanes with Thiochalcones: A Diastereoselective Access to Tetrahydrothiepines

A general approach is described for the formation of tetrahydrothiepines using donor-acceptor cyclopropanes. Thiochalcones, functioning as sulfur-containing four-atom building blocks, were reacted in a Lewis acid catalyzed formal (4 + 3)-cycloaddition reaction with donor-acceptor cyclopropanes as three-atom building blocks. Under mild conditions various tetrahydrothiepines were synthesized in good yields in a stereospecific reaction with high functional group tolerance

Synthesis of Bis-Heterocyclic 1H-Imidazole 3-Oxides from 3-Oxido-1H-imidazole-4-carbohydrazides

The reaction of 1H-imidazole-4-carbohydrazides 1, which are conveniently accessible by treatment of the corresponding esters with NH2NH2·H2O, with isothiocyanates in refluxing EtOH led to thiosemicarbazides (= hydrazinecarbothioamides) 4 in high yields (Scheme 2). Whereas 4 in boiling aqueous NaOH yielded 2,4-dihydro-3H-1,2,4-triazole-3-thiones 5, the reaction in concentrated H2SO4 at room temperature gave 1,3,4-thiadiazol-2-amines 6. Similarly, the reaction of 1 with butyl isocyanate led to semicarbazides 7, which, under basic conditions, undergo cyclization to give 2,4-dihydro-3H-1,2,4-triazol-3-ones 8 (Scheme 3). Treatment of 1 with Ac2O yielded the diacylhydrazine derivatives 9 exclusively, and the alternative isomerization of 1 to imidazol-2-ones was not observed (Scheme 4). It is important to note that, in all these transformations, the imidazole N-oxide residue is retained. Furthermore, it was shown that imidazole N-oxides bearing a 1,2,4-triazole-3-thione or 1,3,4-thiadiazol-2-amine moiety undergo the S-transfer reaction to give bis-heterocyclic 1H-imidazole-2-thiones 11 by treatment with 2,2,4,4-tetramethylcyclobutane-1,3-dithione (Scheme 5)

Temperature-dependent polymorphism of N-(4-fluorophenyl)-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide: experimental and theoretical studies on intermolecular interactions in the crystal state

X-ray analysis of N-(4-fluorophenyl)-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide reveals the temperature-dependent polymorphism associated with the crystallographic symmetry conversion. The observed crystal structure transformation corresponds to a symmetry reduction from I41 /a (I) to P43 (II) space groups. The phase transition mainly concerns the subtle but clearly noticeable reorganization of molecules in the crystal space, with the structure of individual molecules left almost unchanged. The Hirshfeld surface analysis shows that various intermolecular contacts play an important role in the crystal packing, revealing graphically the differences in spatial arrangements of the molecules in both polymorphs. The N-oxide oxygen atom acts as a formally negatively charged hydrogen bonding acceptor in intramolecular hydrogen bond of N–H…O− type. The combined crystallographic and theoretical DFT methods demonstrate that the observed intramolecular N-oxide N–H…O hydrogen bond should be classified as a very strong charge-assisted and closed-shell non-covalent interaction